ALBANY -- State Attorney General Eric Schneiderman vowed Monday to sue the federal government if it fails to study environmental impacts of natural gas hydrofracking before allowing drilling within the Delaware River watershed.

Schneiderman's words were aimed at drilling regulations proposed last year by the Delaware River Basin Commission, which controls the Delaware watershed in New York, New Jersey, Pennsylvania and Delaware.

In New York, the commission covers portions of Broome, Chenango, Delaware, Schoharie, Greene, Ulster, Orange and Sullivan counties. The area includes reservoirs that provide about half the drinking water used by over 9 million New York City residents and visitors.

Hydrofracking is a gas drilling technique that relies on a high-pressure mix of chemicals, water and sand injected deep underground to fracture rock formations and free trapped bubbles of natural gas, which rise to the surface.

Opponents say hydrofracking in other states has caused contamination of ground water, as well as disposal problems with contaminated fracking fluid that returns to the surface. The industry counters that such cases are unproven and the technique is safe.

In 2010, over the objection of then-Gov. David Paterson, the Delaware commission proposed regulations to allow hydrofracking in its territory.

New York is still finalizing its own hydrofracking rules, which are expected to be issued later this year by the state Department of Environmental Conservation. The gas industry is eyeing the state's gas-rich Marcellus Shale formation, which includes most of the Southern Tier -- including the Delaware River watershed.

An industry group questioned the AG's stance. "There is no reason to believe that the DRBC might somehow do other than what it always has done -- protect water quality and water supply," an Independent Oil and Gas Association of New York statement said.

Schneiderman said the Delaware commission estimated up to 18,000 gas wells could be drilled within the entire watershed, with most of them utilizing hydrofracking.

In a letter to the commission, the attorney general demanded that it should immediately suspend consideration of its proposal and conduct "a full review of all public health and safety risks."

He further demanded that the commission study the option of not authorizing natural gas development within the portion of the watershed that includes New York City's reservoir system west of the Hudson River. Previous decisions by the state DEC raised the bar for hydrofracking in that region to make it almost unfeasible for companies.